Azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane
FIELD OF THE INVENTION 
     This invention relates to azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane. These mixtures are useful in a variety of vapor degreasing, cold cleaning and solvent cleaning applications including defluxing. 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     Co-pending, commonly assigned patent application Ser. No. 297,467, filed Jan. 17, 1989, now U.S. Pat. No. 4,894,176, which is a continuation-in-part application of Ser. No. 290,124, filed Dec. 27, 1988, now abandoned, discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and methanol. 
     Co-pending, commonly assigned patent application Ser. No. 345,732, filed May 1, 1989, discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; nitromethane; and methanol or ethanol. 
     Co-pending, commonly assigned patent application Ser. No. 412,080, filed Sept. 25, 1989, discloses azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; methanol; and cyclopentane. 
     Co-pending, commonly assigned patent application Ser. No. 417,134, filed Oct. 4, 1989, now U.S. Pat. No. 4,965,011, discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and nitromethane. 
     Co-pending, commonly assigned patent application Ser. No. 423,993, filed Oct. 19, 1989, discloses azeotrope-like compositions of dichlorotrifluoroethane and methanol. 
     Co-pending, commonly assigned patent application Ser. No. 435,842, filed Nov. 10, 1989, now U.S. Pat. No. 4,960,535, azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and a mono- or di-chlorinated C 2  or C 3  alkane. 
     Co-pending, commonly assigned patent application Ser. No. 435,923, filed Nov. 10, 1989, discloses azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; methanol; and a mono- or di-chlorinated C 2  or C 3  alkane. 
     Co-pending, commonly assigned patent application Ser. No. 453,449, filed Dec. 20, 1989, discloses azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and methyl formate. 
     BACKGROUND OF THE INVENTION 
     Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils. 
     In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent. 
     For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing. 
     Vapor degreasers suitable in the above-described operations are well known in the art. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancillary equipment. 
     Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents and allowed to air dry. 
     Fluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing applications and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts and the like. 
     The art has looked towards azeotrope or azeotrope-like compositions including the desired fluorocarbon components such as trichlorotrifluoroethane which include components which contribute additionally desired characteristics, such as polar functionality, increased solvency power, and stabilizers. Azeotropic or azeotrope-like compositions are desired because they do not fractionate upon boiling. This behavior is desirable because in the previously described vapor degreasing equipment with which these solvents are employed, redistilled material is generated for final rinse-cleaning. Thus, the vapor degreasing system acts as a still. Unless the solvent composition exhibits a constant boiling point, i.e., is azeotrope-like, fractionation will occur and undesirable solvent distribution may act to upset the cleaning and safety of processing. Preferential evaporation of the more volatile components of the solvent mixtures, which would be the case if they were not azeotrope-like, would result in mixtures with changed compositions which may have less desirable properties, such as lower solvency towards soils, less inertness towards metal, plastic or elastomer components, and increased flammability and toxicity. 
     The art is continually seeking new fluorocarbon based azeotrope-like mixtures which offer alternatives for new and special applications for vapor degreasing and other cleaning applications. Currently, of particular interest, are fluorocarbon based azeotrope-like mixtures which are considered to be stratospherically safe substitutes for presently used fully halogenated chlorofluorocarbons. The latter are suspected of causing environmental problems in connection with the earth&#39;s protective ozone layer. Mathematical models have substantiated that hydrochlorofluorocarbons, such as 1,1-dichloro-1-fluoroethane (HCFC-141b) and dichlorotrifluoroethane (HCFC-123 or HCFC-123a), will not adversely affect atmospheric chemistry, being negligible contributors to ozone depletion and to green-house global warming in comparison to the fully halogenated species. Both HCFC-141b and dichlorotrifluoroethane are known to be useful as solvents. 
     Commonly assigned U.S. Pat. No. 4,836,947 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane and ethanol. Commonly assigned U.S. Pat. No. 4,842,764 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane and methanol. Commonly assigned U.S. Pat. No. 4,863,630 discloses azeotrope-like mixtures of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and ethanol. 
     Kokai Patent Publication No. 103,686, published Apr. 20, 1989, discloses an azeotropic mixture of 55 to 80 weight percent dichlorotrifluoroethane and 20 to 45 weight percent 1,1-dichloro-1-fluoroethane. Kokai Patent Publication No. 138,300, published May 31, 1989, discloses a flux cleaning agent of an azeotrope of 67 weight percent 1,1-dichloro-2,2,2-trifluoroethane and 33 weight percent 1,1-dichloro-1-fluoroethane, plus hydrocarbons, alcohols, ketones, and chlorinated hydrocarbons. 
     Kokai Patent Publication No. 139,104, published May 31, 1989, discloses a solvent of an azeotropic mixture of 67 weight percent 1,1-dichloro-2,2,2-trifluoroethane and 33 weight percent 1,1-dichloro-1-fluoroethane, plus hydrocarbons, alcohols, ketones, chlorinated hydrocarbons, and surfactants. Kokai Patent Publication No. 139,861, published Jun. 1, 1989, discloses a dry-cleaning agent of 67 weight percent 1,1-dichloro-2,2,2-trifluoroethane and 33 weight percent 1,1-dichloro-1-fluoroethane, plus hydrocarbons, alcohols, ketones, chlorinated hydrocarbons, and surfactants. 
     Kokai Patent Publication No. 136,981, published May 30, 1989, discloses a degreasing cleaning agent of an azeotropic mixture of 67 weight percent 1,1-dichloro-2,2,2-trifluoroethane and 33 weight percent 1,1-dichloro-1-fluoroethane, plus hydrocarbons, alcohols, ketones, chlorinated hydrocarbons, and esters. Kokai Patent Publication No. 136,982, published May 30, 1989, discloses a buff-grinding cleaning agent of an azeotropic mixture of 67 weight percent 1,1-dichloro-2,2,2-trifluoroethane and 33 weight percent 1,1-dichloro-1-fluoroethane, plus hydrocarbons, alcohols, ketones, chlorinated hydrocarbons, and esters. 
     It is an object of this invention to provide novel azeotrope-like compositions based on HCFC-141b and dichlorotrifluoroethane which are liquid at room temperature, which will not fractionate substantially under the process of distillation or evaporation, and which are useful as solvents for use in vapor degreasing and other solvent cleaning applications including defluxing applications. 
     Another object of the invention is to provide novel environmentally acceptable solvents for use in the aforementioned applications. 
     Other objects and advantages of the invention will become apparent from the following description. 
     DESCRIPTION OF THE INVENTION 
     In accordance with the invention, novel mixtures have been discovered comprising 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane. Also, novel azeotrope-like or constant-boiling compositions have been discovered comprising 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane. The dichlorotrifluoroethane component can be one of its isomers: 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123); 1,2-dichloro-1,1,2-trifluoroethane (HCFC-123a); or mixtures thereof in any proportions. 
     The preferred isomer of dichlorotrifluoroethane is HCFC-123. Preferably, &#34;commercial HCFC-123&#34; which is available as &#34;pure&#34; HCFC-123 containing about 90 to about 95 weight percent of HCFC-123, about 5 to about 10 weight percent of HCFC-123a, and impurities such as trichloromonofluoromethane, trichlorotrifluoroethane, and methylene chloride which due to their presence in insignificant amounts, have no deleterious effects on the properties of the azeotrope-like compositions, is used. &#34;Commercial HCFC-123&#34; is also available as &#34;ultra-pure&#34; HCFC-123 which contains about 95 to about 99.5 weight percent of HCFC-123, about 0.5 to about 5 weight percent of HCFC-123a, and impurities as listed above. 
     Preferably, the novel azeotrope-like compositions comprise effective amounts of 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane. The term &#34;effective amounts&#34; as used herein means the amount of each component which upon combination with the other component, results in the formation of the present azeotrope-like composition. 
     When the dichlorotrifluoroethane used is 1,1-dichloro-2,2,2-trifluoroethane, novel azeotrope-like compositions preferably comprise 1,1-dichloro-1-fluoroethane; 1,1-dichloro-2,2,2-trifluoroethane; and dichloromethane which boil at about 31.8° C. ± about 0.4° C. at 760 mm Hg (101 kPa). 
     Novel azeotrope-like compositions also preferably comprise from about 55 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 41 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; and from about 0.5 to about 4 weight percent of dichloromethane which boil at about 31.8° C. at 760 mm Hg (101 kPa). 
     Preferably the azeotrope-like compositions of the invention comprise from about 62 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 35 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; and from about 0.5 to about 3 weight percent of dichloromethane. 
     Most preferably, the azeotrope-like compositions of the invention comprise from about 65.5 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 32 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; and from about 0.5 to about 2.5 weight percent of dichloromethane. 
     Because the boiling point of 1,1-dichloro-2,2,2-trifluoroethane is 27.8° C. and the boiling point of 1,2-dichloro-1,1,2-trifluoroethane is 29.9° C., it is believed that azeotrope-like compositions of 1,2-dichloro-1,1,2-trifluoroethane; 1,1-dichloro-1-fluoroethane; and dichloromethane would form. It should be understood that the aforementioned compositional ranges for azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; 1,1-dichloro-2,2,2-trifluoroethane; and dichloromethane also apply to azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; 1,2-dichloro-1,1,2-trifluoroethane; and dichloromethane. 
     Because the boiling point of 1,1-dichloro-2,2,2-trifluoroethane is so close to the boiling point of 1,2-dichloro-1,1,2-trifluoroethane, it is also believed that azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; a mixture of 1,1-dichloro-2,2,2-trifluoroethane and 1,2-dichloro-1,1,2-trifluoroethane; and dichloromethane would form. Preferably, the azeotrope-like compositions comprise from about 55 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 21 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; from about 1 to about 20 weight percent of 1,2-dichloro-1,1,2-trifluoroethane; and from about 0.5 to about 4 weight percent of dichloromethane. 
     More preferably, the azeotrope-like compositions comprise from about 62 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 21 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; from about 1 to about 20 weight percent of 1,2-dichloro-1,1,2-trifluoroethane; and from about 0.5 to about 3 weight percent of dichloromethane. 
     Most preferably, the azeotrope-like compositions comprise from about 65.5 to about 98.5 weight percent of 1,1-dichloro-1-fluoroethane; from about 1 to about 21 weight percent of 1,1-dichloro-2,2,2-trifluoroethane; from about 1 to about 20 weight percent of 1,2-dichloro-1,1,2-trifluoroethane; and from about 0.5 to about 2.5 weight percent of dichloromethane. 
     As previously noted, the preferred dichlorotrifluoroethane component is &#34;commercial HCFC-123&#34;. 
     The azeotrope-like compositions of the invention containing a mixture of HCFC-123 and HCFC-123a are azeotrope-like in that they are constant-boiling or essentially constant-boiling. It is not known whether this is the case because the separate ternary azeotrope-like compositions with HCFC-123 and HCFC-123a have boiling points so close to one another as to be indistinguishable for practical purposes or whether HCFC-123 and HCFC-123a form a quaternary azeotrope with 1,1-dichloro-1-fluoroethane and dichloromethane. 
     All compositions within the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below. 
     The precise azeotrope compositions have not been determined but have been ascertained to be within the above ranges. Regardless of where the true azeotropes lie, all compositions with the indicated ranges, as well as certain compositions outside the indicated ranges, are azeotrope-like, as defined more particularly below. 
     It has been found that these azeotrope-like compositions are on the whole nonflammable liquids, i.e. exhibit no flash point when tested by the Tag Open Cup test method--ASTM D 1310-86. 
     From fundamental principles, the thermodynamic state of a fluid is defined by four variables: pressure, temperature, liquid composition and vapor composition, or P-T-X-Y, respectively. An azeotrope is a unique characteristic of a system of two or more components where X and Y are equal at the stated P and T. In practice, this means that the components of a mixture cannot be separated during distillation, and therefore are useful in vapor phase solvent cleaning as described above. 
     For the purpose of this discussion, azeotrope-like composition is intended to mean that the composition behaves like an azeotrope, i.e. has constant-boiling characteristics or a tendency not to fractionate upon boiling or evaporation. Thus, in such compositions, the composition of the vapor formed during boiling or evaporation is identical or substantially identical to the original liquid composition. Hence, during boiling or evaporation, the liquid composition, if it changes at all, changes only to a minimal or negligible extent. This is to be contrasted with non-azeotrope-like compositions in which during boiling or evaporation, the liquid composition changes to a substantial degree. 
     Thus, one way to determine whether a candidate mixture is &#34;azeotrope-like&#34; within the meaning of this invention, is to distill a sample thereof under conditions (i.e. resolution--number of plates) which would be expected to separate the mixture into its separate components. If the mixture is non-azeotrope-like, the mixture will fractionate, i.e. separate into its various components with the lowest boiling component distilling off first, and so on. If the mixture is azeotrope-like, some finite amount of a first distillation cut will be obtained which contains all of the mixture components and which is constant-boiling or behaves as a single substance. This phenomenon cannot occur if the mixture is not azeotrope-like, i.e. it does not behave like an azeotrope. Of course, upon distillation of an azeotrope-like composition such as in a vapor degreaser, the true azeotrope will form and tend to concentrate. 
     It follows from the above that another characteristic of azeotrope-like compositions is that there is a range of compositions containing the same components in varying proportions which are azeotrope-like or constant-boiling. All such compositions are intended to be covered by the term azeotrope-like or constant-boiling as used herein. As an example, it is well known that at differing pressures, the composition of a given azeotrope-like composition will vary at least slightly as does the boiling point of the composition. Thus, an azeotrope-like composition of A and B represents a unique type of relationship but with a variable composition depending on temperature and/or pressure. With 1,1-dichloro-1-fluoroethane; 1,1-dichloro-2,2,2-trifluoroethane; and dichloromethane, the mixtures boil within ± about 0.4° C. (at about 760 mm Hg (101 kPa)) of the 31.8° C. boiling point. As is readily understood by persons skilled in the art, the boiling point of the azeotrope-like composition will vary with the pressure. 
     The azeotrope-like compositions of the invention are useful as solvents in a variety of vapor degreasing, cold cleaning and solvent cleaning applications including defluxing. 
     In one process embodiment of the invention, the azeotrope-like compositions of the invention may be used to clean solid surfaces by treating said surfaces with said compositions in any manner well known to the art such as by dipping or spraying or use of conventional degreasing apparatus. 
     The 1,1-dichloro-1-fluoroethane; dichlorotrifluoroethane; and dichloromethane components of the novel solvent azeotrope-like compositions of the invention are known materials. Preferably, except for &#34;commercial HCFC-123&#34; and its impurities, the materials should be used in sufficiently high purity so as to avoid the introduction of adverse influences upon the desired properties or constant boiling properties of the system. 
     It should be understood that the present compositions may include additional components so as to form new azeotrope-like or constant-boiling compositions. Any such compositions are considered to be within the scope of the present invention as long as the compositions are constant-boiling or essentially constant-boiling and contain all of the essential components described herein. 
    
    
     The present invention is more fully illustrated by the following non-limiting Examples. 
     EXAMPLES 1-2 
     These examples confirm the existence of constant-boiling or azeotrope-like compositions of 1,1-dichloro-1-fluoroethane; 1,1-dichloro-2,2,2-trifluoroethane; and dichloromethane via the method of distillation. It also illustrates that these mixtures do not fractionate during distillation. 
     A 5-plate Oldershaw distillation column with a cold water condensed automatic liquid dividing head was used for these examples. For each Example, the distillation column was charged with HCFC-141b, commercially available ultra-pure HCFC-123, and dichloromethane in the amounts indicated in Table I below for the starting material. Each composition was heated under total reflux for about an hour to ensure equilibration. A reflux ratio of 3:1 was employed for these particular distillations. Approximately 50 percent of the original charges were collected in four similar-sized overhead fractions. The compositions of these fractions were analyzed using gas chromatography. The averages of the distillate fractions and the overhead temperatures are quite constant within the uncertainty associated with determining the compositions, indicating that the mixtures are constant-boiling or azeotrope-like. 
     
                       TABLE I                                                     
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Starting Material (wt. %)                                                 
Example                                                                   
       HCFC-14lb HCFC-123   DICHLOROMETHANE                               
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1      88.90      9.99      1.11                                          
2      74.34     24.63      1.03                                          
Distillate Compositions (wt. %)                                           
Example                                                                   
       HCFC-14lb HCFC-123   DICHLOROMETHANE                               
______________________________________                                    
1      87.97     11.08      0.96                                          
2      71.74     27.55      0.97                                          
                 Barometric    Boiling Point                              
       Boiling   Pressure(mmHg)                                           
                               Corrected to                               
Example                                                                   
       Point (°C.)                                                 
                 (kPa)         760 mmHg(101kPa)                           
______________________________________                                    
1      30.7      739.5(99)     31.5                                       
2      31.3      739.5(99)     32.0                                       
                               Mean 31.8 ± 0.4                         
______________________________________                                    
 
    
     From the above examples, it is readily apparent that additional constant-boiling or essentially constant-boiling mixtures of the same components can readily be identified by anyone of ordinary skill in this art by the method described. No attempt was made to fully characterize and define the outer limits of the composition ranges which are constant-boiling. Anyone skilled in the art can readily ascertain other constant-boiling or essentially constant-boiling mixtures containing the same components. 
     EXAMPLE 3 
     Example 1 is repeated except that 1,2-dichloro-1,1,2-trifluoroethane is used instead of 1,1-dichloro-2,2,2-trifluoroethane. 
     EXAMPLE 4 
     Example 1 is repeated except that a mixture of 1,1-dichloro-2,2,2-trifluoroethane and 1,2-dichloro-1,1,2-trifluoroethane is used instead of 1,1-dichloro-2,2,2-trifluoroethane. 
     Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims.